Conventionally, at the time of deceleration of a vehicle, fuel cut for stopping fuel supply to an internal combustion engine has been performed. By performing fuel cut, useless fuel consumption can be restrained. Meanwhile, however, there are various problems concerning fuel cut. For example, there is the problem of how to restrain the torque shock which occurs at the time of execution of fuel cut, and torque shock which occurs at the time of return from fuel cut. Furthermore, control of deceleration of a vehicle when fuel cut is carried out is one of the problems.
In order to solve these problems, various inventions have already been made. For example, Japanese Patent Laid-Open No. 2001-271690 discloses the invention which has an object to solve the problem of restraining the torque shock which occurs at the time of execution of fuel cut. According to the invention, the ignition time is delayed prior to fuel cut, and thereby, the output torque of the internal combustion engine directly before the fuel cut is reduced. Further, Japanese Patent Laid-Open No. 2006-328984 discloses the invention for restraining the torque shock which occurs at the time of return from fuel cut. The invention intends to prohibit the throttle opening from being controlled to the opening corresponding to a requested acceleration degree while the inner pressure of an intake pipe is larger than target intake pipe inner pressure at the time of cancellation of fuel cut. According to the invention disclosed in Japanese Patent Laid-Open No. 2004-251171, operation of a throttle is performed in accordance withthe target throttle opening which is set based on the target torque so that an optimal engine braking force can be obtained while fuel cut is implemented.
Here, the problem of the invention disclosed in Japanese Patent Laid-Open No. 2004-251171 will be discussed. In the invention, control of torque (minus torque to be a braking force) is performed by using pumping loss, and therefore, even during implementation of fuel cut, the throttle is not always fully closed. Therefore, it can happen that the throttle is open at the time point when the fuel cut is cancelled. As for cancellation of fuel cut, fuel cut is suddenly cancelled by the operation of an accelerator pedal of a driver and the intervention of the control system of a vehicle. When fuel cut is cancelled in the state in which the throttle is open, combustion is restarted from the state in which much air is in an intake pipe, and therefore, unintentional excessive torque is suddenly outputted. More specifically, the invention disclosed in Japanese Patent Laid-Open No. 2004-251171 has the problem of the possibility of occurrence of a torque shock accompanying return from fuel cut.
As the solution of this problem, for example, application of the invention disclosed in Japanese Patent Laid-Open No. 2006-328984 is conceivable. However, the invention is effective in the one in which the throttle is closed during implementation of fuel cut, but does not always obtain a sufficient effect in the one in which the throttle is operated during implementation of fuel cut. This is because the throttle is sometimes open at the time point when the fuel cut is cancelled in the latter, and in such a case, the inner pressure in the intake pipe never decreases sufficiently how long one may wait. Accordingly, the invention disclosed in Japanese Patent Laid-Open No. 2006-328984 cannot be used as the solution to the problem which belongs to the invention disclosed in Japanese Patent Laid-Open No. 2004-251171.